Using more than 150 Chandra observations spread over 13 years, researchers identified a bonanza of stellar-mass black holes, that is, those that form from the collapse of a giant star and typically have masses between five and 10 times that of the Sun. // X-ray: NASA/CXC/SAO/R. Barnard, Z. Lee, et al.; Optical: NOAO/AURA/NSF/REU Program/B. Schoening, V. Harvey and Descubre Foundation/CAHA/OAUV/DSA/V. Peris